The invention generally relates to a subsea intervention system.
Subsea wells are typically completed in generally the same manner as conventional land wells. Therefore, subsea wells are subject to the same service requirements as land wells. Further, services performed by intervention can often increase the production from the well. However, intervention into a subsea well to perform the required service is extremely costly. Typically, to complete such an intervention, the operator must deploy a rig, such as a semi-submersible rig, using tensioned risers. Thus, to avoid the costs of such intervention, some form of xe2x80x9clightxe2x80x9d intervention (one in which a rig is not required) is desirable.
Often, an operator will observe a drop in production or some other problem, but will not know the cause. To determine the cause, the operator must perform an intervention. In some cases the problem may be remedied while in others it may not. Also, the degree of the problem may only be determinable by intervention. Therefore, one level of light intervention is to ascertain the cause of the problem to determine whether an intervention is warranted and economical.
A higher level of light intervention is to perform some intervention service without the use of a rig. Shutting in a zone and pumping a well treatment into a well are two examples of many possible intervention services that may be performed via light intervention.
Although some developments in the field, such as intelligent completions, may facilitate the determination of whether to perform a fig intervention, they do not offer a complete range of desired light intervention solutions. In addition, not all wells are equipped with the technology. Similarly, previous efforts to provide light intervention do not offer the economical range of services sought.
A conventional subsea intervention may involve use a surface vessel to supply equipment for the intervention and serve as a platform for the intervention. The vessel typically has a global positioning satellite system (GPS) and side thrusters that allow the vessel to precisely position itself over the subsea well to be serviced. While the vessel holds its position, a remotely operated vehicle (ROV) may then be lowered from the vessel to find a wellhead of the subsea well and initiate the intervention. The ROV typically is used in depths where divers cannot be used. The ROV has a tethered cable connection to the vessel, a connection that communicates power to the ROV; communicates video signals from the ROV to the vessel; and communicates signals from the vessel to the ROV to control the ROV.
A typical ROV intervention may include using the ROV to find and attach guide wires to the wellhead. These guidewires extend to the surface vessel so that the surface vessel may then deploy a downhole tool or equipment for the well. In this manner, the deployed tool or equipment follows the guide wires from the vessel down to the subsea wellhead. The ROV typically provides images of the intervention and assists in attaching equipment to the wellhead so that tools may be lowered downhole into the well.
The surface vessel for performing the above-described intervention may be quite expensive due to the positioning capability of the vessel and the weight and size of the equipment that must be carried on the vessel. Thus, there is a continuing need for an arrangement that addresses one or more of the problems that are stated above.
In an embodiment of the invention, a system that is usable with subsea wells that extend beneath a sea floor includes a station that is located on the sea floor and an underwater vehicle. The vehicle is housed in the station and is adapted to service at least one of the subsea wells.